1. Field of the Invention
In general, the present invention relates to counterbalance systems for windows that prevent open window sashes from moving under the force of their own weight. More particularly, the present invention system relates to the structure of the brake shoe component of counterbalance systems for tilt-in windows and the manner in which springs connects to the brake shoe.
2. Description of the Prior Art
There are many types and styles of windows. One of the most common types of window is the double-hung window. Double-hung windows are the window of choice for most home construction applications. A double-hung window consists of an upper window sash and a lower window sash. Either the upper window sash or the lower window sash can be selectively opened and closed by a person sliding the sash up and down within the window frame.
A popular variation of the double-hung window is the tilt-in double-hung window. Tilt-in double-hung windows have sashes that can be selectively moved up and down. Additionally, the sashes can be selectively tilted into the home so that the exterior of the sashes can be cleaned from within the home.
The sash of a double-hung window has a weight that depends upon the materials used to make the window sash and the size of the window sash. Since the sashes of a double-hung window are free to move up and down within the frame of a window, some counterbalancing system must be used to prevent the window sashes from constantly moving to the bottom of the window frame under the force of their own weight.
For many years, counterbalance weights were hung next to the window frames in weight wells. The weights were attached to window sashes using a string or chain that passed over a pulley at the top of the window frame. The weights counterbalanced the weight of the window sashes. As such, when the sashes were moved in the window frame, they had a neutral weight and friction would hold them in place.
The use of weight wells, however, prevents insulation from being packed tightly around a window frame. Furthermore, the use of counterbalance weights on chains or strings cannot be adapted well to tilt-in double-hung windows. Accordingly, as tilt-in windows were being developed, alternative counterbalance systems were developed that were contained within the confines of the window frame and did not interfere with the tilt action of the tilt-in windows.
Modern tilt-in double-hung windows are primarily manufactured in one of two ways. There are vinyl frame windows and wooden frame windows. In the window manufacturing industry, different types of counterbalance systems are traditionally used for vinyl frame windows and for wooden frame windows. The present invention is mainly concerned with the structure of vinyl frame windows. As such, the prior art concerning vinyl frame windows is herein addressed.
Vinyl frame, tilt-in, double-hung windows are typically manufactured with guide tracks along the inside of the window frame. Brake shoe assemblies, commonly known as “shoes” in the window industry, are placed in the guide tracks and ride up and down within the guide tracks. Each sash of the window has two tilt pins or tilt posts that extend into the shoes and cause the shoes to ride up and down in the guide tracks as the window sashes are opened or closed.
The shoes contain a brake mechanism that is activated by the tilt post of the window sash when the window sash is tilted inwardly away from the window frame. The shoe therefore locks the tilt post in place and prevents the base of the sash from moving up or down in the window frame once the sash is tilted open. Furthermore, the brake shoes are attached to curl springs inside the guide tracks of the window assembly. Curl springs are constant force coil springs, made from wound length of metal ribbon, that supply the counterbalance force needed to suspend the weight of the window sash.
Small tilt-in windows have small relatively light window sashes. Such small sashes may only require a single coil spring on either side of the window sash to generate the required counterbalance forces. However, due to the space restrictions present in modern tilt-in window assemblies, larger springs cannot be used for heavier window sashes. Rather, multiple smaller coil springs are ganged together to provide the needed counterbalance force. A large tilt-in window sash may have up to eight coil springs to provide the needed counterbalance force. Counterbalance systems that use ganged assemblies of coil springs are exemplified by U.S. Pat. No. 5,232,208 to Braid, entitled Springs For Sash Frame Tensioning Arrangements.
The metal ribbons of coil springs in a window counterbalance system usually experience tension as they support the weight of the window sash. However, this is not always the case. When a window sash is rapidly opened, the upward speed of the window sash may exceed the recoil speed of the counterbalance springs. In such a situation, the metal ribbons of the coil springs may experience a brief period of compression. The ribbons of coil springs are typically uniform in width, except for the free ends of the spring ribbon. The free ends of the spring ribbon are often stamped and shaped so that the end of the spring can engage the structure of the brake shoe. Since the areas near the ends of the spring ribbons are reduced in width, the repeating tension and compression stresses tend to concentrate in these reduced areas. The cycles of tension forces and compressive forces cause the metal ribbon of the coil spring to fatigue. Eventually, the fatigue forces can cause the coil spring to break, thereby disconnecting the coil spring from the brake shoe. This causes the overall counterbalance system to fail.
A need therefore exists in the field of vinyl, tilt-in, double-hung windows, for a counterbalance system with a brake shoe that can attach to a coil spring in such a way that the structure of the brake shoe prevents fatigue stresses from compromising the coil spring. This need is met by the present invention as described and claimed below.